Hydraulic machines such as dozers, loaders, excavators, backhoes, motor graders, and other types of heavy equipment use one or more hydraulic actuators to accomplish a variety of tasks. These actuators are fluidly connected to a pump of the machine that provides pressurized fluid to chambers within the actuators. As the pressurized fluid moves into or through the chambers, the pressure of the fluid acts on hydraulic surfaces of the chambers to affect movement of the actuators and a connected work tool. When the pressurized fluid is drained from the chambers it is returned to a low-pressure sump of the machine.
One problem associated with this type of hydraulic arrangement involves efficiency. In particular, the fluid draining from the actuator chambers to the sump often has a pressure greater than a pressure of the fluid already within the sump, especially when the actuators are moving in a direction aligned with the pull of gravity (i.e., when actuator movement is being assisted by a weight of the tool and associated load). As a result, the higher pressure fluid draining into the sump still contains some energy that is wasted upon entering the low-pressure sump. This wasted energy reduces the efficiency of the hydraulic system.
One attempt to improve the efficiency of a hydraulic machine is disclosed in U.S. Patent Publication No. 2014/0026550 of Brinkman et al, that published on Jan. 30, 2014 (“the '550 publication”). In particular, the '550 publication discloses a hydraulic system having a boom cylinder, and an accumulator connected to receive fluid from the boom cylinder during lowering of a boom. The hydraulic system also has a fan motor connected to the accumulator via an independent metering valve. The accumulator is configured to selectively discharge accumulated fluid to drive the fan motor, thereby recovering energy that would otherwise be lost. A charge pump is configured to provide makeup fluid to the fan motor and to a pilot supply.
Although the system of the '550 publication may help to improve efficiencies in some situations through storage and reuse of pressurized fluid, it may still be improved upon. In particular, there may be other components and/or circuits of the hydraulic system that could benefit from use of the accumulated fluid, and the '550 publication does not disclose how to share the fluid between competing components or circuits.
The disclosed hydraulic system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.